I recently finished a room that's (mostly) dedicated to brewing, and I thought I'd spruce it up with some quick-reference posters. One thing I thought would be handy/fun would be a list of gotcha's that can be relatively easily avoided if you practice good brewing techniques.

There have been numerous posts suggesting how to avoid problem X with resolution Y. But they're spread all over the place, and the resolutions are generally pretty drawn out. It would be handy to have a thread that's dedicated to a quick-list of common problems and how to avoid them. If further explanation is necessary, we can provide links to the original discussion.

So what are common gotcha's that you try to avoid? I'm looking for anything, from "Remember to take the lid off your BK once it starts boiling" to "Avoid hot-side aeration" etc.

(As a side-note: let's try to limit debates over whether a particular "gotcha" is worth worrying about. Ideally, I'd like to adhere to good brewing techniques that will avoid most of the pit-falls regardless of whether they're truly necessary or have been blown out of proportion. If it's relatively easy to follow and could avoid a head-ache, it's worth following. And if it's worth following, it's worth putting on a poster. HSA, for example: perhaps it's blown out of proportion. But it's relatively easy to avoid splashing hot wort, so it's probably worth making part of your brewing technique.)

As this will go on a poster, I'd prefer the gotcha be relatively brief. I'll start:

Take the BK lid off!
Once the BK comes to a boil, take the lid off to ensure that sulfure compounds (DMS) are boiled off

Avoid Hot-Side Aeration!
HSA can lead to beer going stale. It occurs when hot wort (above 86*) is exposed to oxygen, typically as a result of splashing.